Caloplaca coralloides

A Question: What are the bumps surrounding some
apothecia?

There are frequently bumps on the surface of the thallus of C.
coralloides. Many of these bumps have a hole in the center.
Sectioning did not definitively determine the identity of these bumps
for me, because they showed only that the bumps had cortex and medulla.
Here I give a hypothesis as to the identity of these bumps. If you
know what these structures are or if you can help me figure them
out, contact Megan Kelso at mkelso@stanford.edu or Judith Connor
at MBARI.

This is a scanning electron
micrograph of an apotheciaof C. coralloides and a zoomed
in look at a bump on the edge
of the apothecia. Picture taken
by Megan Kelso with the help
of Chris Patton.

Hypothesis as to the identity of the bumps on the thallus
and surrounding some apothecia:

These bumps might be apothecia in early stages of development.
Maybe they will open up from the pore in the center of the bump and
develop into apothecia. Sectioning the bumps did not show a developed
hymenial layer, however, it is possible that it had just not developed
yet. Younger looking apothecia do not have prominent bumps. Therefore,
it is possible that the bumps only develop on older apothecia that
have perhaps already released their spores. Pictures taken by Chris
Patton and Megan Kelso of apothecia in different stages suggest that
this is the identity of the bumps.

It is also possible that these bumps are simply nodules
filled with medulla that form on the thalline surfaces of C. Coralloides. However,
I cannot help but think that the central hole seen in some of the bumps
indicates a purpose. It is also possible that both are true:
that some of the bumps are developing apothecia and that others are
simply thalline nodules.

Another thought was that the bumps could be pycnidia. This
would make sense because having the "spermatia" released right next
to the fertile layer of the apothecia would help encourage successful
sexual reproduction. However, the bumps seem like they might
be too large to be pycnidia.

These bumps could also be lobules, a structure for asexual
reproduction that sometimes appear around the rims of apothecia. See
the section on asexual reproduction for
a little moreinformation on lobules.

Overall, my best guess is that these bumps are new apothecia
just beginning to develop.